Question

A reactor is supplied with 5 moles of C4H10, and it undergoes following reactions C4H10 + 4H2O -> 4CO + 9H2 and C4H10 + 6.5O2 -> 4CO2 + 5H2O, if 8 moles of CO2 was produced and 2 moles of C4H10 remains unreacted, what are the number of moles of CO produced?

(a) 1

(b) 2

(c) 3

(d) 4

This question was addressed to me at a job interview.

My enquiry is from Processes Involving Multiple Units in section The Chemical Reaction Equation & Stoichometry, Material Balances for Processes Involving Reaction and Multiple Units of Basic Chemical Engineering

Answer 1

Let's break down the given problem step by step to find the number of moles of CO produced.

Given:

• 5 moles of C₄H₁₀ (butane) are supplied to the reactor.
• The following reactions occur:
  1. C₄H₁₀ + 4H₂O → 4CO + 9H₂
  2. C₄H₁₀ + 6.5O₂ → 4CO₂ + 5H₂O
• 8 moles of CO₂ are produced.
• 2 moles of C₄H₁₀ remain unreacted.

We need to determine the number of moles of CO produced.

Step 1: Define variables

Let:

• x be the number of moles of C₄H₁₀ that react according to the first reaction (C₄H₁₀ + 4H₂O → 4CO + 9H₂).
• y be the number of moles of C₄H₁₀ that react according to the second reaction (C₄H₁₀ + 6.5O₂ → 4CO₂ + 5H₂O).

Step 2: Material balances

• The total moles of C₄H₁₀ reacting:

  $$x+y=5-2=3(\text{since 2 moles of C₄H₁₀ remain unreacted})$$

• The moles of CO₂ produced are given as 8, and the second reaction produces 4 moles of CO₂ for every mole of C₄H₁₀ reacting. Therefore, the total moles of CO₂ produced is:

  $$4y=8\Rightarrow y=2$$

• Now substitute $y=2$ into the first equation:

  $$x+2=3\Rightarrow x=1$$

Step 3: Calculate the moles of CO produced

From the first reaction, for every mole of C₄H₁₀, 4 moles of CO are produced. Therefore, the number of moles of CO produced is:

$$\text{Moles of CO}=4\times x=4\times 1=4$$

Final Answer:

The number of moles of CO produced is:

(d) 4.